In multicast operation, multicast packets associated with a particular multicast group, from a particular source, enter a router at a specific ingress interface. Conventional multicast forwarding mechanisms constrain the forwarding of the multicast packets destined to the same group, from the same destination, on the incoming interface. As such, under normal operating conditions for a given source and group, packets never exit on the ingress interface.
For example, IPTV (Internet Protocol television) uses multicast routing and forwarding technologies to carry video traffic from servers to set-top boxes (STBs) which connect to a TV. It is difficult for service providers to avoid any delay in screen refresh or minimize traffic loss due to any topology change or network down events. PIM (Protocol Independent Multicast) Dual Join is a functionality that enables a multicast network to minimize traffic loss in the event of an inoperative link on the path through which the multicast traffic is being received. This technology draws multicast data for a specific (S, G) route from multiple upstream interfaces. One of these two interfaces is typically referred to as the primary interface and the other interface is typically referred to as the secondary interface.
When the primary path fails, traffic received on the secondary path is used to serve interested hosts. However, conventional implementations of the PIM Dual Join mechanism are limited to star and square network topologies even though ring topologies are one of the most widely deployed topologies. If the conventional PIM Dual Join technology is used on a ring topology, then the functionality to serve hosts with multicast traffic from the secondary path when the primary path fails is not achieved. Indeed, the MoFRR (Multicast only Fast ReRoute) draft put forth by the IETF (Internet Engineering Task Force) that specifies fast re-route functionality for multicast traffic does not include support for ring topologies. As such, the secondary interface conventionally does not receive multicast traffic for ring topologies. When the primary interface goes down, multicast traffic is therefore lost to all hosts and downstream routers until the route is converged and traffic flow resumed via a newly established routing tree based on the PIM (Protocol-Independent Multicast) protocol. This delay is not acceptable for many types of applications including IPTV.